Hawthorne et al has reported the preparation of closo-1,12-C2B10(CH3)12 and other octamethyl C2 boranes.(Jiang, W., Knobler, C. B., Mortimer, M. D., Hawthorne, M. F., Angew. Chem., 1995, 34, 1332.). The permethylated icosahedral carboranes [closo-CB11(CH3)12]31 , and the uncharged blue radical closo-CB11(CH3)12 derived from that anion, has been reported by Michl et al. (King, B. T., Zanousek, B. G., Trammell, M., Noll. B. C., Michl, J., J Am. Chem. Soc., 1996, 118, 3313) Additionally, other persubstituted polyboron compounds are known.
The most prominent persubstituted polyboron compounds is the polyhydroxylated boron compound, boric acid, B(OH)3. Alkaline solutions of B(OH)3 deposit Na2[B4O5(OH)4]xc2x7nH2O, which constitute two abundant boron minerals, kernite (n=2) and borax (n=8) (F. A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th ed., Wiley, New York, 1988, pp. 164-169). Other common boron structures include the trigonal and tetrahedral boron-oxygen units common to borate minerals (G. A. Heller, Top. Curr. Chem. 1986, 131, 39-98) and the icosahedron. The allotropes of elemental boron, (J. Donohue, The Structures of the Elements, Wiley, New York, 1974, pp. 48-82), boron-rich solids (H. Hubert, B. Devouard, L. A. J. Garvie, M. O""Keeffe, P. R. Buseck, W. T. Petuskey, P. F. McMillan, Nature 1998, 391, 376-378) and the parent anion of the polyhedral boranes, [closo-B12H12]2xe2x88x92 (J. A. Wunderlich, W. N. Lipscomb, J Am. Chem. Soc. 1960, 82, 4427-4428) all contain B12 icosohedra.
The charge-delocalized icosohedral ion [closo-B12H12]2xe2x88x92 may be considered as the parent aromatic species for borane chemistry in a manner similar to that served by the benzene ring in organic (carbon) chemistry. Isoelectronic substitution of one or two :B-H vertices in [closo-B12H12]2xe2x88x92 by :C-H+ provides the aromatic derivatives [closo-1-CB11H12]xe2x88x92, and a set of three isomeric dicarbacarboranes (1,2xe2x88x92 or ortho; 1,7xe2x88x92 or meta; and 1,12xe2x88x92 or para) closo-C2B10H12 R (N. Grimes, Carboranes, Academic Press, New York, 1970, p. 8). Each of these isoelectronic derivatives of [closo-B12H12]2xe2x88x92, undergoes characteristic hydrogen-substitution reactions at their B-H vertices resulting in a huge number of known icosohedral species (Hawthorne, M. F., xe2x80x9cCarborane Chemistry at Work and Playxe2x80x9d, Proceedings of the Ninth International Meeting on Boron Chemistry published in Advances in Boron Chemistry, Seibert, W. (Ed.), The Royal Society of Chemistry, London, 1996, 261-272)
Of special interest are derivatives in which every available B-H vertex has been substituted. Thus, hydrophobic derivatives of [closo-B12H12]2xe2x88x92 and [closo-1-CB11H12]xe2x88x92, and the three isomeric diboranes, such as [closo-B12Cl12]2xe2x88x92 (Knoth, W. H., Miller, H. C., Sauer, J. C., Balthis, J. H., Chia, Y. T., Muetterties, E. L., Inorg, Chem, 1964, 3, 159-167), [closo-CB11(CH3)12]xe2x88x92, (King, B. T.; Janousek, Z.; Grxc3xcner, B.; Trammell, M.; Noll, B. C.; Michl, J. J. Am. Chem. Soc. 1996, 118, 10902-10903) and closo-1,12-C2B10(CH3)12, (W. Jiang, C. B. Knobler, M. D. Mortimer, M. F. Hawthorne, Angew. Chem. 1995, 107, 1470-1473; Angew. Chem. Int. Ed. Engl. 1995, 34, 1332-1334.) have been synthesized. The existence and formulation of similar highly substituted polyhedral borane derivatives having hydrophilic substituents, such as hydroxyl have most recently been demonstrated by Hawthorne and Peyman (xe2x80x9cAromatic Polyhedra Hydroxyborates: Bridging Boron Oxides and Boron Nitridesxe2x80x9d, Angew. Chem. Int. Ed., 1999,38,1061-1064).
U.S. Pat. No. 3,551,120 to Miller, et.al. discloses the formation of numerous ionic icosahedral substituted boranes of the general formula Ma(B12H12-yXy)b, with y=1-12, and U.S. Pat. No. 3,390,966 to Knofl et. al. discloses the formation of numerous ionic carboranes of the general formula Ma(B10H10-yXy)b, with y=1-10, where b=1 to 3. However, examples of the analogous closo-borane dianions [closo-Bn(CH3)n]2xe2x88x92 (n=6-12) have not been reported.
Paramagnetic persubstituted polyhedral closo-boranes such as [closo-B6X6]xe2x88x92 (Heinrich, A, Keller, H. L., Preetz, W. Z. Naturforsch., Teil B., 1990, 45, 184) and [closo-B9X9]xe2x88x92 (Wong, E. H., Kabbani, R. M., Inorg. Chem., 1990, 45, 184) where X is Cl, Br or I and [closo-CN11Me12]xe2x88x92 (B. T. King, B. T., Noll, B. C., McKinley, A. J., Michl, J., J. Am. Chem. Soc., 1996. 118. 10902) have also been reported. These species were obtained via metal-ion oxidation of the corresponding reduced borane clusters. In each case, solutions of these paramagnetic species are moderately stable, but decolorize after prolonged contact with air.
Many researchers have sought globular structures possessing both hydrophobic surfaces and extraordinary kinetic stability with which to synthesize supramolecular structures, weakly-coordinating anions and space-controlling drug components. The fullerenes, characterized by unique chemistry and physical properties, represent one family of such precursors. Another family of globular hydrophobes, referred to as xe2x80x9ccamouflagedxe2x80x9d carboranes, have been described in the literature (Jiang, W.; Knobler, C. B.; Hawthorne, M. F. Angew. Chem., Int. Ed. Engl. 1995, 34, 1332-1334; King, B. T.; Janousek, Z.; Grxc3xcner, B.; Trammell, M.; Noll, B. C.; Michl, J. J. Am. Chem. Soc. 1996, 118, 3313-3314; Herzog, A.; Maderna, A.; Knobler, C. B.; Hawthorne, M. F. Chem. Eur. J. 1999, 5,1212-1217). These species may approach the van der Waals diameter of C60 by attachment of methyl groups and functionalized methyl substituents to the icosahedral scaffolding of the aromatic [closo-CnB12xe2x88x92nH12]nxe2x88x922 (n=1 or 2). Whereas hydrophobic and amphiphilic derivatives of this sort are known with n=1 or 2, the fully methylated derivative of the parent species, dodecamethyl-closo-dodecaborate(2xe2x88x92), (n=0), has not been shown.